Saturday, January 30, 2010

The Mk 13 torpedo that the Navy used throughout World War II was developed in the early 1930s and placed in service in 1935, when the carrier-based torpedo bombers were still biplanes, although the new Douglas TBD had just flown for the first time. Unfortunately, due to budget constraints, it was not fully qualified for realistic drop speeds and altitudes and the operation of its firing mechanisms was more theoretical than proven. When the war began, the Mk 13 proved disappointing. Even if the obsolescent TBD got in close enough to drop one, it was unlikely to run straight and if it did and hit the enemy ship, was even less likely to detonate. (Submariners experienced the same problems with the Mk 13's depth control and exploders.)

Note: the above is a museum display that shouldn't be used as a color reference.

On the TBD, the Mk 13 was carried externally. Operational pictures taken prior to the Midway torpedo attack disaster indicate that the warhead section was gray, probably the same color as the bottom of the TBD, while the rest of the body was brass colored.

By then, a wooden "box" had been developed to improve the ballistics of the torpedo so it entered the water cleanly and at the desired angle. The box would break off when the torpedo hit the water. Unlike the later tail box, it had scolloped sides with a square or rectangular top and bottom inclined at an angle to the longitudinal axis of the torpedo (the edge of the fins was not angled so it wasn't inclined for that reason).

This is a picture of a test of this box in October 1941. Note the scalloped side panels and the thickness of the upper and lower sides.

However, the torpedo was still unreliable and had to be dropped at too low a speed and altitude for survivability.

An extensive development and qualification program resulted in a very satisfactory weapon by 1944. The only external change to the torpedo itself was the ring tail, which improved the stability of the torpedo in the water so it ran straight at the set depth.

In addition, a new set of plywood appendages was added to improve the torpedo's stability in the air and eliminate damage when it hit the water. The wooden barrel on the nose was called the drag ring. It slowed the torpedo from the drop speed prior to water entry and also acted as a shock absorber. The plywood box on the tail was redesigned and simplified. Both of these wooden structures were designed to break away when the torpedo hit the water.

The later torpedoes may have had an olive drab warhead, the same as bombs, and a more silvery power unit.

The TBD's successor, the TBF/TBM Avenger, carried the torpedo in a bomb bay so the well-described drag ring was not a problem. The subsequent attack airplanes, the AD Skyraider and the AM Mauler, were to carry the torpedo externally. To reduce drag, a streamlined nose cap was developed that was pulled off by a lanyard when the torpedo was dropped.

However, the nose cap wasn't used for the last combat torpedo drop on the sluice gates at the Hwachon Dam during the Korean War.

In January 1943, the U.S. Navy released a specification that replaced the simple blue-gray over light gray camouflage scheme scheme with a complex one that employed counter-shading and counter-shadowing. Simply put, a dark blue was applied to the surfaces viewed from the top, a lighter blue on surfaces viewed from the side, and white on surfaces viewed from the bottom. As might be expected, there was a changeover period during which some aircraft that had already been delivered in the superseded scheme were repainted.

There appears to have been an early implementation of the concept at the Navy's Norfolk, Virginia aircraft rework/repair facility which differed from the more generally accepted approach with respect to the amount of light blue versus dark on the side of the fuselage. The most obvious difference is the demarcation of the dark blue extending upward from the wing on to the side of the fuselage. In what I call the Norfolk scheme, 1) the width of the dark blue area narrows above the wing instead of expanding forward and aft and 2) less of the top of the fuselage is dark blue. This F4U Corsair is an example:

There are pictures of just about every carrier-based airplanes in the Norfolk scheme variation:

Note that aircraft in this scheme lasted through the various national insignia changes that occurred through July 1943. However, the attrition of carrier-based aircraft combined with the overhaul of survivors resulted in this scheme disappearing very quickly. Here is a picture of Norfolk-scheme Hellcats aboard Yorktown along with one in the better known tri-color scheme:

This air group features Avengers in three different schemes. Also notable is the thin white stripe running up the cowling, which appears to be an aid for lineup during a torpedo attack.

Saturday, January 9, 2010

23 March 2017: Rich Scheuerer noted that I didn't get this right the first time. He referred me to this link: http://maritime.org/doc/ordnance/index.htm for Navy and Army munitions, OP-1644 along with the following comments: The Navy and Army developed their own bombs separately, but the Navy
let Army ordnance continue with bomb development. Bombs were signal
yellow and light gray until April 15, 1942, then became the Army Ground
Forces OD, not OD-41. OD-41 is a AAC/AAF color. AGF OD became
standardized as ANA-613. The Navy and Army had great quantities of
yellow bombs in stock so they were still dropping yellow bombs over
Europe and the Aleutians into 1943.I haven't had a chance to revise what I wrote so proceed with caution hereafter:

I’m by no means an expert on this but I’ve spent a little time researching the subject and haven’t seen anything much better on the internet so far. The best single dissertation that I have seen is in Replica In Scale, Volume 2, No. 3 & 4, Spring and Summer 1974. It doesn’t however, include some of the details below on US Navy bombs.

Some people think that overall yellow denoted practice or inert bombs. According to the Replica In Scale article, Demolition, Incendiary, and Fragmentation bombs were painted dull, flat Yellow during 1920's-1930's. Practice Bombs below 100 pounds were flat white with one two inch blue band; over 100 pounds had a four inch band.

My guess is that bombs were delivered at the beginning of the WWII were still being delivered with a yellow primer coat for corrosion protection and then painted to suit. Here is an August 1943 picture of bombing up a PV-1 in the Aleutians. Note that there is a yellow bomb on the bomb truck. The others seem to be typical of 500 pound bombs - Dark Olive Drab (OD)* with a yellow band around the tail and the nose where the fuse goes, with a thin yellow band in the middle, presumably denoting the center of gravity. (The nose and tail band denoted the explosive in the bomb.) Note that the OD bomb closest to the camera on the bomb cart has a much weathered tail fin box compared to the one behind it. Normally the tail fin box was pristine, since it was shipped in a crate to prevent damage to the fins and ofter stored inside, separately from the bombs. Bombs and box fins from different manufacturers or manufacturing batches might very well be mated in the field, resulting in not only a difference in the "newness" of the bomb and box fin, but in color as well.

Somewhat earlier in the war, US Navy bombs seem to have been painted light gray with no bands, the gray presumably to match the camouflage of the light gray aircraft underside. There is a yellow circle between the mounting lugs, however, which is where the most useful bomb data, e.g. the ammunition lot number, was marked. This picture was taken next to a very early TBF in mid 1942. Note that the fins are oriented at 45 degrees to the usual position. Again, the fins appear to be more pristine than the bomb body.

Another gray bomb, this time for a PBY in January 1943. Note the even more pristine tail fins compared to the rusted? bomb body and the yellow circle on top.

There are several B&W pictures of Doolittle's 500# bombs from early 1942 - They are a light color, presumably gray (since they were probably Navy bombs provided by Hornet) but they could be yellow, and have lots of stencil type markings and mid-section bands.

Looking at the pictures I have so far, it seems that the 500# OD colored bombs had a single thin yellow stripe denoting the center of gravity and the 1000# bombs had a faint red-brown band that corresponded with each of the two suspension lugs instead. This band results from discoloration by the packing band that surrounded the bomb for transportation.

The tail fin orientation depended on the aircraft. Supposedly, the tail fins were generally installed "flat" when the bomb was to be hung externally and "pointed" (rotated 45 degrees so one of the fins aligned with the suspension lugs) when hung from an internal bomb rack. Here are 1000(?)# bombs with vertical fins ready for loading on a B-29; also note the two red-brown bands that are oriented on the lugs as mentioned above and the stenciling between the lugs:

There isn’t much consistency about the fin orientation in pictures so far. In the pictures above, the bomb in front of the TBF has the fins vertical but in instructional pictures of the TBF bomb bay with bombs in it, the fins are “flat”. The fins in the picture of the PV-1 loadout are also oriented "flat" and it has a bomb bay. It's also not clear to me why having the fins vertical was necessary other than a bomb with fins that way might have slightly better directional stability when initially dropped, which if true would be important when dropping them side-by-side and close together so they wouldn't "bump" below the aircraft. Otherwise it seems that having the fins "flat" is an advantage - slightly better ground clearance when on the cart, clearance with the aircraft when installed on a pylon, and better bomb-to-bomb clearance when stacked vertically in a bomb bay.

Here is a good picture of a Mk 43 500# bomb with the vertical fin orientation that also shows the standard markings including stenciling except for that thin yellow band around the middle denoting the center of gravity - you'll note in the picture of the "gray" bombs above that there is a circle of yellow (probably chromate) between the lugs, which is where the production Lot Number goes, probably the only important data on the bomb when it gets to the field.** That's why I think the bombs were painted yellow during production up through the beginning of the war and field painted. Gray would have been the logical color for the Navy since that was the color of the bottom of their aircraft. My guess is that OD from the bomb manufacturing factory became standard with the Army and Navy both using the same color bombs. Why OD? Probably because when they're out in the open prior to being loaded they're not such an obvious target. That might have been important to somebody in the Army and the Navy could lump it and paint their bombs if they wanted.

*You're on your own with respect to what color OD is. At the beginning of the war, it was presumably Dark Olive Drab 41, which was pretty dark. However, the actual shade appears to have varied quite a bit, not only when applied but after only a little exposure in the field. It was replaced later in the war by ANA 613, which by some reports is lighter and either browner or greener, but one wonders whether the bomb manufacturers were told to change in any event.

**The wording aft of the forward lug is something like LOT 1234/EXPLOSIVE/BOMB; The four digit number is representative. The wording forward of the aft lug is FROM PICATINNY ARSENAL; the O's forward of that would be a date or something like P.A. 12-43.

About Me

In 1956, at age 12, I lived on NAS Sangley Point in the Philippine Islands. Always enamored with airplanes, I imprinted on the Cougars, Banshees, and Skyraiders then being deployed. Not able to be a Naval Aviator because I was nearsighted, I instead became an aeronautical engineer and general aviation pilot. Now retired, I write books and monographs on U.S. Navy aircraft.